This invention relates to a transparent substrate. More particularly, the present invention relates to a hydrophobic, oil-phobic and/or contamination-free transparent substrate such as motor vehicle and building window glasses, windshields, optical lenses and glass lenses etc.
In order to prevent contamination of a transparent substrate such as glass, it has been proposed to make the surface of the transparent substrate as smooth as possible or coat the substrate surface with a protective film such as a fluorine-based coating film or the like. Further, to prevent fogging of the transparent substrate surface, a hydrophilic polymer is coated thereon, or a heater is installed in or onto the transparent substrate.
Where the contamination of a transparent substrate stems from water drops, an antifogging effect can be obtained by installing a heater. However, the use of a heater has a drawback, namely a power source for the heater is necessary. Furthermore, a heater which is buried in or installed on the surface of the transparent substrate may reduce the transparency thereof. Coating the transparent substrate surface with a hydrophilic polymer or the like is comparatively simple. However, only a tentative effect is achieved because the hydrophilic polymer may be peeled off by rubbing the transparent substrate surface.
Where contamination of the substrate surface stems from other causes the above methods are substantially meaningless. Accordingly, it has been proposed to coat the transparent substrate surface with a protective film, for example fluorine-based coatings. However, the adhesion between the transparent substrate and a fluorine-based protective film is weak. Therefore the film is readily separated from the substrate surface. In addition, the fluorine-based protective film causes fogging of the transparent substrate due to its opaqueness. Other protective film materials can improve upon the transparency and adhesion of the flourine-based protective films. However, these materials do not enable easily wiping-out of contaminants. Accordingly, it is a practical method to make the surface of the transparent substrate as smooth as possible. However, there are limitations on the degree of smoothness of the substrate surface which one skilled in the art can attain. Thus, there is a need for a contamination free, hydrophobic and/or oil phobic treated transparent substrate.
An object of the present invention is to provide a highly hydrophobic and contamination free transparent substrate, which is free from the attachment of contaminants thereon or is capable of the ready removal of any attached contaminants.
To attain this object, the instant invention provides a transparent substrate, which is provided on at least one surface thereon with a chemically adsorbed monomolecule film containing a hydrophobic group.
A first aspect of this invention provides a transparent substrate comprising at least one monomolecule film formed as an outer most surface layer on at least one surface of a transparent substrate either directly or indirectly via a protective film. The monomolecule film contains a hydrophobic group and is bonded through covalent bonding to the surface of the substrate or of the protective film. Preferably, the protective film is itself one or more of such monomolecule films containing a hydrophobic group and bonded through a covalent bond to the surface of the substrate. A difference between the (a) monomolecule film of the protective film and (b) the outer most surface layer monomolecule film is that (a) is at or near the end of the hydrophobic group and the protective film monomolecule is bonded through a covalent bond to (b), the outer most surface layer monomolecule film. Another difference is that (b) is bonded to the protective layer monomolecule film one layer closer to the outer most surface. One preferred embodiment of the first aspect of this invention provides a transparent substrate comprising a monomolecule film formed as an outer surface layer on both surfaces of a transparent substrate either directly or indirectly via a protective film. In particular, one of the surfaces (the first surface) is covered with a monomolecule film containing a hydrophobic group which is covalently bonded to the first surface. The other surface (the second surface) is covered with a monomolecule film containing a hydrophilic group which is covalently bonded to the second surface.
According to another embodiment of the first aspect of this invention, the monomolecule film is formed by a covalent bond from a silane halide-based or alkoxy silane-based surface-active compound of the formula:
F(CF2)m(CH2)nSiRqX3-qxe2x80x83xe2x80x83(A)
where m represents an integer ranging from 1 to 15, n represents an integer ranging from 0 to 15, the sum of m and n ranges from 10 to 30, q represents an integer ranging from 0 to 2, R represents an alkyl or an alkoxyl group. and X is a halogen atom or an alkoxyl group; or
F(CF2)mxe2x80x2(CH2)nxe2x80x2A(CH2)pSi RqX3-qxe2x80x83xe2x80x83(B)
where mxe2x80x2 represents an integer ranging from 1 to 8, nxe2x80x2 represents an integer ranging from 0 to 2 p represents an integer ranging from 5 to 25, q represents an integer ranging from 0 to 2, X represents a halogen atom or an alkoxyl group, R represents an alkyl or an alkoxyl group, and A represents xe2x80x94Oxe2x80x94, a xe2x80x94COOxe2x80x94 or xe2x80x94Si(CH3)2xe2x80x94.
A second aspect of this invention provides a method of modifying a transparent substrate, comprising:
applying, in a non-aqueous organic solvent, a silane based surface active molecular compound having a reactive silane group at one end of the molecular compound and a hydrophobic group at the other end of the molecular compound to a surface of a transparent substrate or on a surface of a protective film provided on the transparent substrate. The molecular compound is applied under conditions such that the silane-based surface active compound is chemically adsorbed on the surface thereby forming a monomolecule film on the transparent substrate. The film comprises a hydrophobic group, an xe2x80x94Sixe2x80x94 group wherein the film is covalently bonded to the applied surface.
One preferred embodiment of the second aspect of this invention provides such a method which comprises:
contacting a surface of a molded transparent substrate with an organic solvent solution of a silane-based surface active compound having a reactive silane group at one end of the molecule and a hydrophobic group at the other end of the molecule to form a chemically adsorbed monomolecule film of the silane-based surface active compound on at least one surface of the transparent substrate or over the entire surface area.
Another preferred embodiment of the second aspect of this invention provides such a method which comprises:
contacting both of the surfaces of the molded transparent substrate with a non-aqueous solvent containing a material having at least two chlorosilyl groups;
washing the transparent substrate using a non-aqueous organic solution to remove any non-reacted material having at least two chlorosilyl groups of the transparent substrate after the contacting step;
treating the transparent substrate with water after the non-reacted material washing step, thereby forming a hydrophilic monomolecule film composed of a silane material having at least one silanol group; and
treating the transparent substrate having the silanol group with a silane-based surface active compound having a reactive silane group at one end of the molecule and a hydrophobic group at the other end of the molecule, thereby laminating a chemically adsorbed hydrophobic monomolecule film on the hydrophilic monomolecule film having silanol groups.